1. Field of the Invention
The present invention relates to a tape position and reel rotation detection method for a video cassette tape recorder (VCR) capable of detecting top and end positions of a tape, a supply reel rotation, and a take-up reel rotation by alternatively performing a tape position detection operation and a reel rotation detection operation and by time-sharing a detection signal with respect to the tape position detection operation and the reel rotation detection operation, thus reducing the number of input ports of a microprocessor.
2. Description of the Conventional Art
FIG. 1 shows a tape position and reel rotation detection apparatus of a conventional VCR, which includes a microprocessor 100 for generating a series of pulses, detecting detection signals SS1 through SS4 inputted to first through fourth input ports PI1 through PI4, and detecting top and end positions of a tape and a supply reel rotation, a first switching device 101 for periodically switching in accordance with a pulse outputted from the microprocessor 100 and for outputting a signal corresponding to the switching, a start detection position detection unit 103 for detecting a start position of the tape in accordance with a signal outputted from the first switching device 101 and for outputting a detection signal SS1 to the start position detection unit 103 of the microprocessor 100, an end position detection unit 104 for detecting an end position of the tape in accordance with a signal outputted from the first switching device 101 and for outputting a detection signal SS2 to the second input port PI2 of the microprocessor 100, a second switching device 102 for periodically switching in accordance with a pulse outputted from the microprocessor 100 and for outputting a signal corresponding to the switching, a supply reel rotation detection unit 105 for detecting the rotation of the supply reel in accordance with a signal outputted from the second switching device 102 and for outputting a detection signal SS3 to the input port PI3 of the microprocessor 100, and a take-up reel rotation detection unit 106 for detecting the rotation of the take-up reel in accordance with a signal outputted from the second switching device 102 and for outputting a detection signal SS4 to the fourth input port PI4 of the microprocessor 100.
The start position detection unit 103 includes a first light emitting device LED1 mined on in accordance with a signal outputted from the first switching device 101 and for emitting light signal, and a first light receiving device PT1 for detecting a start position of the tape at the time of receiving light of a light signal transmitted from the first light emitting device LED1 and for outputting a detection signal SS2 to the second input port PI2 of the microprocessor 100.
The supply reel rotation detection unit 105 includes a second light emitting device LED2 turned on in accordance with a signal outputted from the second switching device 102 and for outputting light signal, and a third light receiving device PT3 for detecting the rotation of the supply reel in accordance with a light signal outputted from the second light emitting device LED2 and for outputting a detection signal SS3 to the third input port PI3 of the microprocessor 100.
The take-up reel rotation detection unit 106 includes a third light emitting device LED3 turned on in accordance with a signal outputted from the second switching device 102 and for outputting light signal, and a fourth light receiving device PT4 for detecting the rotation of the take-up reel in accordance with a light signal transmitted from the third light emitting device LED3 and for outputting a detection signal SS4 to the fourth input port PI4 of the microprocessor 100.
In addition, FIG. 5 shows a flow chart of a tape position and reel rotation detection method for a conventional VCR, which includes the steps of a first step which turning off (S1) the first light emitting device LED1 through the third light emitting device LED3 for a predetermined time t1 at a reproducing mode or at a recording mode, a second step which turns on the light emitting device LED1 through the light emitting device LED3 for a predetermined time t2 after the predetermined time t1 is lapsed, detects the detection signals SS1 through SS4 inputted to the first through fourth input ports PI1 through PI4, and detects the start and end positions of the tape, the take-up reel rotation, and the supply reel rotation.
The operation of the tape position and reel rotation detection apparatus of a conventional VCR will now be explained with reference to the accompanying drawings.
To begin with, at the initial stage, the microprocessor 100 outputs a high level signal for a predetermined time t1 through the first and second output ports PO1 and PO2 as shown in FIG. 2.
Thereafter, the first switching device 101 is turned off in accordance with a signal outputted from the microprocessor 100, and the first light emitting device LED1 of the start position detection unit 103 and the end position detection unit 104 are turned off as the first switching device 101 is turned off.
In addition, the second switching device 102 is turned off in accordance with a high level signal outputted from the second output port PO2 of the microprocessor 100, and the second light emitting device LED2 of the supply reel rotation detection unit 105 and the third light emitting device LED3 of the take-up reel rotation detection unit 106 are turned off (S1), respectively, as the second switching device is turned off.
Thereafter, when a predetermined time t1 is lapsed, the microprocessor 100 outputs a low level signal for a predetermined time t2 through the first and second output ports PO1 and PO2.
As light signal is transmitted from the first light emitting device LED1, the first and second light receiving devices PT1 and PT2 detect the start and end positions of the tape in accordance with a light emitting state of the light signal.
In more detail, while the tape is spooled from the supply reel 107 to the take-up reel 108 and wound onto the take-up reel 108 through post guides 110 and 111 and a drum 109, when a transparent part of the tape is appeared, the light signal transmitted from the first light emitting device LED1 passes through the transparent part of the tape, and is transmitted to the light receiving device PT1, and the first light receiving device PT1 is turned on.
As the first light receiving device PT1 is turned on, the first light receiving device PT1 outputs a low level detection signal SS1, and the microprocessor 100 detects (S4) the detection signal SS1 of a low level applied thereto through the first input port PI1 and detects the start position of the tape.
Thereafter, when the spool from the supply reel 107 to the take-up reel 108 is finished, that is, the transparent part appears, the light signal transmitted from the first light emitting device LED1 passes through the transparent part of the tape and is transmitted to the light receiving device PT2, and the microprocessor 100 detects (S4) a low level signal inputted to the second input port PI2 and detects the end position of the tape.
In addition, the switching device 102 is turned on in accordance with a low level signal outputted from the second output port PO2 of the microprocessor 100, and the second and third light emitting devices LED2 and LED3 are turned on (S3), respectively, and transmit light signals.
As shown in FIG. 4, the light signal transmitted from the second light emitting device LED2 is transmitted to the fourth light receiving device PT4 in cooperation with a receiving plate 113 and a reflection plate 114 of the supply reel plate 112. The light receiving device PT3 is turned off or turned on and outputs a high level signal or a low level signal to the third input port PO3 of the microprocessor 100.
Therefore, the microprocessor 100 detects (S4) the high level signal and the low level signal outputted from the light receiving device PT3 and detects the rotation of the supply reel.
In addition, since the fourth light receiving device PT4 has the same operation as the third light receiving device PT3, the microprocessor 100 detects the high level signal and the low level signal outputted from the fourth input port PI4 and detects the rotation of the take-up reel.
After a predetermined time t2 is lapsed, the microprocessor 100 performs the steps S1 through S4 and detects the start and end positions of the tape, the supply reel rotation and the take-up rotation.
However, the tape position and reel rotation detection method of a conventional VCR has disadvantages in that the number of input ports of the microprocessor is increased because the start and end positions of the tape and the supply reel and take-up reel rotations are detected by detecting detections signals with respect to the start and end positions of the tape and the supply reel and take-up reel rotations, respectively. In addition, in case of a VCR having various functions, additional microprocessor is necessary because of the lack of the number of ports.